1. Technical Field
The disclosure relates in general to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having better gate metal filling.
2. Description of the Related Art
With a trend toward scaling down the size of the semiconductor device, work function metals are used to replace the conventional polysilicon gate to be the control electrode that competent to the high-K gate dielectric layer. The conventional dual metal gate methods are categorized into gate first process and gate last process. Among the two main processes, the gate last process is able to avoid processes of high thermal budget and to provide wider material choices for the high-K gate dielectric layer and the metal gate, and thus gradually replaces the gate first process.
However, in the conventional gate last process, barrier layer or strained stress layer is often formed in the gate trench before forming the metals, which reduces an opening width of the gate trench. This makes it difficult to fill the gate trench with the work function metal layer and cause metal gate void issue. Eventually, the electrical performance of the transistor device having the metal gate is deteriorated.